docs: def gateway_snapshot(self, indices=None):
          """
          Gateway snapshot one or more indices
          (See :ref:`es-guide-reference-api-admin-indices-gateway-snapshot`)
  
          :keyword indices: a list of indices or None for default configured.
          """
          path = self.conn._make_path(indices, (), '_gateway', 'snapshot')
          return self.conn._send_request('POST', path)